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calc_areas [2013/07/10 17:17]
admin [Notes] 		calc_areas [2026/08/28 03:09] (current)
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-====== Calc Areas ====== ​+====== Calc Areas ======
  
 ===== Description ===== ===== Description =====
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 ^ Name  ^ Type  ^ Description ​ ^ ^ Name  ^ Type  ^ Description ​ ^
-| Categorical Map  | [[Categorical Map Type|Categorical Map]]  | Map containing ​classes ​or categories.  |+| Source ​ | [[Categorical Map Type]] ​ | Map whose non-null cells correspond to categories or classes. ​ |
  
-===== Output ​=====+===== Optional Inputs ===== 
 + 
 +^ Name  ^ Type  ^ Description ​ ^ Default Value  ^ 
 +| Use Authalic Area  | [[Boolean Value Type]] ​ | If true, the area of each cell in a geographic (Lat/Long) grid is computed using an authalic sphere, which preserves surface area during projection. This improves the accuracy of area calculations across all latitudes by avoiding distortions. If the grid is geographic but this option is false, all cells are treated as having the same area, calculated by treating the length of one degree of latitude or longitude as a constant 111255 meters. This is an advanced port.  | Yes  | 
 + 
 +===== Outputs ​=====
  
 ^ Name  ^ Type  ^ Description ​ ^ ^ Name  ^ Type  ^ Description ​ ^
-| Areas  | [[Table Type|Table]]  | Area of each map category ​in cells, hectares and square meters. ​ |+| Areas  | [[Table Type]] ​ | Area of each source feature, ​in cells, hectares, and square meters. ​ |
  
 ===== Group ===== ===== Group =====
  
-[[Functor List#Map Algebra|Map Algebra]]+[[Functor List#Map Algebra | Map Algebra]]
  
 ===== Notes ===== ===== Notes =====
  
-Only the areas corresponding to class or categories ​defined ​in the input map header ​are calculated.+Only the areas of classes ​or categories ​present ​in Source'​s categorization ​are calculated; other values are ignored.
  
-If the cell dimensions are represented using degrees, the areas in hectares and square meters becomes an approximation. All cells are always supposed to be of the same size. +The resulting ​table has the following format.
- +
-The table containing the resulting ​area has the following format.+
  
 ^ Column Name  ^ Key or Data?  ^ Column Type  ^ Description ​ ^ ^ Column Name  ^ Key or Data?  ^ Column Type  ^ Description ​ ^
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 | "​Area_In_Hectares" ​ | Data  | Real  | Area of corresponding category in hectares ​ | | "​Area_In_Hectares" ​ | Data  | Real  | Area of corresponding category in hectares ​ |
 | "​Area_In_Square_Meters" ​ | Data  | Real  | Area of corresponding category in square meters ​ | | "​Area_In_Square_Meters" ​ | Data  | Real  | Area of corresponding category in square meters ​ |
 +
 +**References**
 +
 +Santini, M., Taramelli, A. and Sorichetta, A., 2010: [[https://​www.researchgate.net/​publication/​220606016_ASPHAA_A_GIS-Based_algorithm_to_calculate_cell_area_on_a_latitude-longitude_Geographic_regular_grid|ASPHAA:​ A GIS-Based Algorithm to Calculate Cell Area on a Latitude-Longitude (Geographic) Regular Grid]]. Transactions in GIS, 14(3), 351-377.
 +
 ===== Internal Name ===== ===== Internal Name =====
  
 CalcAreas CalcAreas
 +
 +===== Usage examples =====
 +
 +See practical examples of this functor in [[lesson_9|Lesson 9: Working with maps and tables]]